The battery pack, which usually incorporates a battery protection/power management circuit, may take an independent form so that it can be detached for recharging or for replacement, or it may be an integrated or built-in component so that it is cannot be removed.
In general, Li-ion batteries are used in battery packs that contain both lithium ion battery cells and battery protection/management circuits. For user replaceable battery packs, both items are enclosed in a container which is usually made of a plastics material so that the battery pack cannot easily be disassembled. The battery protection electronics may be sealed with a material such as resin. For battery packs which are not designed to be replaced by end users, they are integrated within the tools or appliance. One of the major functions of the protection circuit is to avoid the LI-ion battery cells discharging at a voltage below a threshold voltage, such as 3.0 V per cell, because over-discharging may damage or downgrade the performance (i.e. capacity) of the battery pack.
Traditionally, at least one MOSFET (i.e. metal oxide semiconducter field-effect transistor) is integrated in a Li-ion battery pack for protecting the Li-ion battery cells from over-discharging.
The electrical output to an appliance or power tool will be cut off or reduced through the MOSFET integrated in the battery pack when the battery management electronics detect an adverse operating condition that may cause problems to the battery such as over-discharging. This will be accomplished by cutting the power either through the positive battery terminal B+ for a P-channel MOSFET or the negative battery terminal B− for an N-channel MOSFET.
This traditional way of battery protection is however expensive. Moreover, the heat generated/dissipated by the MOSFET by current passing through it may heat up and hence damage or deteriorate the battery cells inside the battery pack.
The invention seeks to mitigate or to at least alleviate such a problem by providing a new or otherwise improved electrical appliance.